This invention relates to a fuel injection pump for an internal combustion engine, such as a diesel engine.
Diesel engines are supplied with fuel by means of fuel injection pumps, which pressurize fuel periodically with respect to rotation of the engine crankshaft to effect fuel injection into the engine combustion chambers at a desired timing. As soon as fuel is injected into the combustion chambers, the fuel encounters highly compressed and heated air so that it burns spontaneously. Thus, the time of the initiation of fuel injection is an essential parameter determining fuel combustion characteristics. The variation of the rate of fuel injection with the rotational angle of the crankshaft during each fuel injection stroke also affects fuel combustion characteristics.
Especially for vehicular engines, desired characteristic curves or patterns of the fuel injection rate versus crank angles depend on the operating conditions of the engine, such as engine load. At lower loads, the fuel injection curve should be platykurtic and skewed toward high crank angles (as shown in FIG. 1) so that the fuel injection quantity, and thus combustion chamber temperature and pressure, build up gradually. This minimizes synthesis of harmful nitrogen oxide (NOx) exhaust. On the other hand, in order to ensure adequate power output, the fuel injection curve at higher loads should be leptokurtic (as shown in FIG. 2) to induce intense combustion. This also minimizes synthesis of undesirable hydrocarbon (HC) exhaust, smoke, and particulates.